40 THE NAUTILUS. 



ON A NEW SPECIES OF MYLLITA. 



BY W. H. DALL. 



The genus Myllita was founded in 1850 by d'Orbiguy and Recluz 

 on a species named by Recluz M. Deshayesii, which was subsequently 

 wrongly united to Pythina Hinds by Adams and others. This 

 error was pointed out by E. A. Smith in a discussion of the genus 

 Pythina in 1891. The original authors wrongly ascribed a tri- 

 angular pallial sinus to Myllita. The name was subsequently 

 changed to Mylitta by Kobelt but there does not seem to be ground 

 for the assumption that the original name was based on that of the 

 city. The essential characters of the genus are as follows : 



Shell small, equivalve, with a small anterior and posterior dorsal 

 gape, with an obsolete external amphidetic ligament and a strong 

 internal resilium, the latter with a mesial calcareous coating ; pallial 

 line simple, with rather large adductor scars ; foot strong, byssifer- 

 ous ; the young incubated, as in Kellia, within the mother's tissues, 

 numerous, vitreous, smooth ; the adult strong, with concentric and 

 radiate or divaricate sculpture, the surface more or less punctate or 

 sagrinate; hinge with, in the left valve single lateral lamina? in 

 front and behind, with a /\ -shaped or petaloid cardinal ; the right 

 valve is similar but with double laterals, the resilium set in a well 

 marked sulcus below the ventral posterior lamina. Type M. 

 Deshayesii Recluz. 



Two species have since been described as Pythina: Myllita tas- 

 manica Tension-Woods (1875) from Tasmania and M. Stowei Hutton 

 (1873) from New Zealand. The former proves from authentic speci- 

 mens to be quite distinct from M. Deshayesii. Smith added, in 

 1891, M. auriculata from Tasmania. 



M. Deshayesii has the right cardinal merely grooved, not /\ -shaped ; 

 in M. tasmanica both are conspicuously /\ -shaped. In M. Stoweifye 

 right cardinal is small, slender and simple, the anterior lamina? very 

 short and stout, the posterior lamina? quite long and slender. The 

 resilium in the latter is rather short, and there is a small impressed 

 lunule over the dorsal anterior lamina. In all, the external ligament 

 is feeble but present and amphidetic. The following new species is 

 in the collection of the Academy of Natural Sciences Philadelphia. 



